1. Related Applications
This application claims priority from British applications GB 9126586.8 filed Dec. 14, 1991 and GB 9212409.8 filed Jun. 11, 1992, both assigned to the assignee of this application, Eaton Corporation.
2. Field of the Invention
The present invention relates to a range shift arrangement for a range type compound transmission and, more particularly, to an automatic range shift arrangement for an otherwise manually shifted range type compound transmission.
3. Description of the Prior Art
Compound transmissions of the range or combined range/splitter type are well known in the prior art as may be seen by reference to U.S. Pat. Nos. 3,105,395; 3,138,965; 3,171,300; 3,283,613 and 4,754,665, the disclosures of which are hereby incorporated by reference.
Briefly, such transmissions typically comprise a multiple speed main transmission section connected in series with a range type auxiliary section wherein the range step is greater than the total ratio coverage of the main transmission section. Assignee's well known RT/RTO 11609 and RT/RTO 11610 "Roadranger" transmissions are examples of "(4+1).times.(2)", nine speed and "(5).times.(2)" ten speed heavy duty range type transmissions.
In such transmissions, the main section is typically shifted by means of a shift bar housing assembly controlled by a manually operated shift lever or the like and the auxiliary range section is shifted by means of button or switch, usually manually operated, which controls a remote slave valve/actuator mechanism. As the range section often utilizes synchronized jaw clutches, to provide acceptable shift quality and prevent undue wear and/or damage to the range section synchronized jaw clutches, a range shift should be initiated, and preferably completed, while the main transmission section is in neutral.
In view of the above, the prior art compound range type transmissions usually include control systems, usually a pneumatic control system including interlock devices, which allowed a range shift to be preselected by use of a selector button or switch at a master control valve but not initiated until the main transmission section is shifted to, or at least towards, the neutral condition. Examples of such transmissions and the control systems therefor may be seen by reference to U.S. Pat. Nos. 2,654,268; 3,138,965, 4,060,005 and 4,974,474, the disclosures of which are hereby incorporated by reference. Range type transmissions utilizing mechanical interlock devices, of both the rigid and the resilient type, may be seen by reference to U.S. Pat. Nos. 4,974,474; 4,944,197 and 4,296,642, the disclosures of which are hereby incorporated by reference.
The prior art manually controlled range type compound transmissions were usually of the "repeat H" type wherein the range shift was selected or preselected by the operator, usually by a button/switch on the shift lever, or of the "double H" type wherein a sensor sensed shifting between "H" patterns to select a range shift. So-called "double H" type controls are well known in the prior art as may be seen by reference to U.S. Pat. Nos. 4,633,725 and 4,275,612, the disclosures of which are hereby incorporated by reference.
While the prior art manually shifted range type compound transmissions are very successful, especially for use in heavy duty vehicles, they are not totally satisfactory as those equipped with "repeat H" type controls require manual selection of the range shift and/or may inadvertently be shifted into an inappropriate range wherein under or over speeding of the engine may occur and those equipped with "double H" type controls may require an excessive amount of shift lever transverse space and/or may be awkward to shift.